ABOUT RETELL AI Retell AI is using first principles to reimagine the call center with cutting-edge voice AI. Since launching 18 months ago, thousands of companies now utilize Retell’s AI voice agents to handle sales, support, and logistics calls that once required large teams of human agents. Backed by Y Combinator, Alt Capital, and other leading investors, we have scaled to $36M ARR with a team of 20 people, up from $5M at the start of 2025. Our vision for 2026 is to build a modern CX platform where entire contact centers are powered by AI. Instead of basic automation that needs constant human tuning, we’re creating intelligent AI “workers” that can act as frontline agents, QA analysts, and managers — continuously executing, monitoring, and improving customer interactions. We’re growing quickly and looking for ambitious builders who want to tackle hard technical problems, move fast, and have real impact at one of the fastest-growing voice AI startups. Let’s build the future together. We’re a top 50 AI app in a16z list: a16z Top AI Apps #4 on Brex's Fast-Growing Software Vendors of 2025: Brex Benchmark 2025 We're also one of the top ranking startups on: Lean AI Leaderboard Enterprise Tech 30: Wing Venture Capital ET30 ABOUT THE ROLE We are seeking a Telephony Engineer to who will own the technical success of our telephony integrations, act as the first line of defense for advanced enterprise telephony support, and drive seamless post-onboarding experiences. Your work will directly impact call quality, reliability, and customer experience. You’ll move fast, collaborate with customers, and help define the gold standard for AI voice infrastructure. KEY RESPONSIBILITIES Integration Ownership: Manage and collaborate with customers to support complex SIP integrations with CCaaS/CPaaS platforms like NiCE, Five9, Avaya, Genesys, Amazon Connect, Twilio, and Telnyx, while driving future platform integrations. Advanced Troubleshooting: Investigate and debug call failures via PCAP analysis, SIP traces, and carrier logs to improve reliability. Enterprise Support Frontline: Act as the primary technical point of contact for enterprise clients post-onboarding. Product Advocacy: Translate customer technical feedback and friction points into actionable product improvements for our development teams. YOU MIGHT THRIVE IF Have 5+ years as a Telephony Engineer, VoIP Engineer, or equivalent low-latency networking role. Have deep understanding of the SIP Protocol (RFC 3261), RTP (media) debugging voice quality issues with PCAPs and trace tools such as Wireshark/TShark. Strong Networking fundamentals.(TCP/IP/TLS, DNS, Firewalls). Familiarity with modern CPaaS/cloud communication platforms (e.g., Twilio, Plivo, Telnyx). Ability to write or modify basic scripts (e.g., Python, Bash, JavaScript). Automate routine troubleshooting tasks. Exceptional ability to guide premium clients through complex setups and communicate technical issues clearly. Familiarity with Asterisk/FreeSWITCH/Kamailio or relevant SIP proxy / SIP servers is a plus. JOB DETAILS Compensation: $25–45/hour USD Location: Fully Remote (Global candidates welcome) Working Hours: Candidates must be comfortable working full-time within US Eastern Time business hours